qtnfmac: request userspace to do OBSS scanning if FW can not

In case firmware reports that it can not do OBSS scanning for 40MHz
2.4GHz channels itself, tell userpsace to do that instead by setting
NL80211_FEATURE_NEED_OBSS_SCAN flag.

Signed-off-by: Igor mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>